Apparatus for opening exhaust and vent ports of an air conditioning unit

ABSTRACT

Apparatus for selectively opening the exhaust and vent ports in a wall between the condenser and evaporator sections of an air conditioning unit, the apparatus comprising hinged doors biased to port closing positions and an operating lever having an actuating arm extending from a rotatable shaft for selectively exerting torque on tabs extending from the doors to open the selected one of the doors.

United States Patent [191 Bolton [451 July 16,1974

[75] Inventor: Theodore S. Bolton, Liverpool, NY.

[73] Assignee: Carrier Corporation, Syracuse, N.Y.

Wright 62/427 Bell 62/427 Primary ExaminerWilliam J. Wye Attorney,Agent, or FirmJ. Raymond Curtin; D. Peter Hochberg [5 7 ABSTRACT 8Claims, 4 Drawing Figures [22] Filed: May 2, 1973 [21] Appl. No.:356,658

[52] US. Cl 62/262, 62/427, 98/94 [51] Int. Cl. F25d 23/12 [58] Field ofSearch 62/262, 427; 98/94, 94 AC [56] References Cited UNITED STATESPATENTS 2,343,122 2/1944 Eberhart 98/94 AC 2,986,016 5/1961 Gillham62/262 PATENTEU JUL! 61874.

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WIHHHIII HIIH APPARATUS FOR OPENING EXHAUST AND VENT PORTS OF AN AIRCONDITIONING UNIT BACKGROUND OF THE INVENTION 1. Field of the InventionThe present invention relates to air conditioning units which areadapted to exhaust stale air from a room being served by the unit andalternatively to vent external air into the room. More specifically, thepres ent invention relates to apparatus for selectively opening andclosing exhaust and vent ports in room air conditioners having theforegoing capability.

2. Description of the Prior Art Air conditioning units such as theso-called selfcontained air conditioning units commonly used forresidential and similar applications, generally include refrigerationcircuits having an evaporator and a condenser. The unit is generallydivided into an evaporator section and a condenser section, and the twosections are isolated from one another by a partition. The unit isnormally mounted with the evaporator section being adjacent to the spacebeing served by the unit and in communication with the air in thatsection, and the condenser section being in communication with externalair such as outdoor air. Refrigerant flows through the refrigerationcircuit and absorbs heat from the room air in the evaporator sectioncausing the refrigerant therein to evaporate and flow towards thecondenser section, where it gives up the absorbed heat to the ambientair flowing over the condenser. In addition to the capability ofcontrolling the temperature of the air in the space being conditioned,it is often desirable to remove stale air from the space or to admitfresh, outdoor air to the space. This is accomplished in various airconditioning units by the provision of appropriately spaced ports in theunit which can be selectively opened and closed to control the flow ofair to and from the conditioned space.

Ports of the aforementioned type can be located to make use of thepressure differentials which usually exist in air conditioning equipmentof the kind described. Conventional self-contained air conditioningunits include a blower wheel positioned adjacent to the evaporator fordrawing room air over the evaporator coils and into the low pressurecenter of the blower wheel, from whence the air passes radiallyoutwardly through the blower wheel to a high pressure region and backinto the room. A fan is generally located adjacent to the condenser ofthe unit for drawing ambient air into the low pressure region created bythe rotating fan blades, and for directing that air over the condensercoils for cooling the refrigerant within the coils. The condenser fanand the evaporator blower are usually in a generally opposingrelationship on opposite sides of the partition dividing the unit intothe condenser section and the evaporator section. The air pressure onthe evaporator side of the partition in the region of the blower wheelis generally lower than the pressure on the opposite side of thepartition because the partition is located closer to the blower wheel.Hence, the provision of a port between the fan and blower wheel wouldenable the admittance of outdoor air through that port into a room beingconditioned. On the other hand, the region above the blower wheelnormally has a very high pressure, and the provision of a port in thepartition above the blower wheel would enable the passage of air out ofthe room and into the condenser section of the unit. The use of suchports is known in the art, as evidenced by US. Pat. No. 2,986,016 whichissued on May 30, 1961 to Gillham et al.

In order to make effective use of the foregoing ports, it is desirableto open only one port at a time to obtain a sufficient flow of airtherethrough. It is additionally desirable to incorporate port closingapparatus which necessitates neither an increase in the size of the unitnor a substantial modification of the components thereof. Likewise, itis desirable to keep the cost of such venting and exhaust apparatus aslow as possible.

Prior mechanisms for opening and closing such vent and exhaust portshave often been relatively complex, requiring numerous parts andconsiderable skill in assembling these parts. Moreover, since it isimportant to maintain a port open once it has been decided to open thatport, the employment of expensive and complicated friction devices hasfrequently been necessary. Also, mechanisms of the preceding type havetended to make access to the interior of the air conditioning unitsdifficult, thus impeding repair work on the unit.

SUMMARY OF THE INVENTION An object of the present invention is toselectively exhaust air from a space being air conditioned or to ventfresh air to that space.

A more specific object of the invention is to adapt an air conditioningunit to exhaust stale air from a room being air conditioned and to ventfresh air into the room.

A still more specific object of the invention is to provide apparatusfor selectively opening and closing vent and exhaust ports in aself-contained air conditioning unit, which apparatus is simple inconstruction, easy-to operate, and economical to manufacture andinstall.

Other objects will be apparent from the description to follow and fromthe appended claims.

The preceding objects are achieved according to a preferred embodimentof the invention by the provision of a pair of pivotally mounted doorsfor selectively opening and closing the vent and exhaust ports in aselfcontained air conditioning unit, and a very simple mechanism foralternatively opening one of the two doors. Each of the doors are springbiased to a port closing position, and each door has a tab to whichforce canbe applied for exerting a torque on the door to open it. Arotatable operating lever selectively engages the tab of one of the twodoors for effecting the opening of the door. The operating lever canadvantageously comprise a rotatable shaft, a first or actuating armextending from the shaft and between the tabs of the two doors, and asecond or control arm extending from the shaft and including a manuallyaccessible portion. The tabs are preferably so configured and biasedthat once the operating lever has been rotated a predetermined amount toopen one of the doors, the tab acts to restrain the lever arm fromreturning to its initial position, whereby the dooris held in its openposition until the manually accessible portion is moved to release thetab.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side view of aself-contained room air conditioning unit.

FIG. 2 is a partial pictorial view of a room air conditioner employingapparatus according to the invention,

portions having been cut away to reveal various components thereof.

FIGS. 3 and 4 are top elevations of the apparatus shown in FIG. 2 atdifferent stages in the operation of the apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT The embodiment of the inventiondescribed below is adapted for use in a self-contained room airconditioning unit, although it is to be understood that the inventionfinds like applicability in other forms of air conditioning units. Theair conditioning unit described below includes a wall or partitionseparating the unit into a condenser or outdoor section whichcommunicates with the outdoor or external air, and an evaporator orindoor section which is in communication with the room being airconditioned. An exhaust port is defined in the foregoing wall at aposition wherein the pressure on the evaporator side of the wall isgreater than that on the condenser side of the wall, and a vent port isprovided at a section of the wall where the pressure on the condenserside of the wall is higher than that on the evaporator side of the wall.Thus, air can be exhausted from the room to the outdoors through theexhaust port by virtue of the pressure differential existing there,while fresh air can be vented into the room by virtue of the pressuredifferential existing across the vent port. A pair of door are pivotallymounted adjacent to each of the ports for opening and closing the ports.A rotatable lever is provided having an arm for exerting force on thedoors to effect the opening thereof, and a manually accessible arm forcontrolling the operation of the lever.

Referring now to the drawings, FIG. 1 shows in schematic form aself-contained room air conditioning unit having appropriately placedexhaust and vent ports. The unit includes a condenser section in whichare located a condenser 1 and a fan 3 for directing ambient air over thecondenser coils as indicated by the arrow, and an evaporator sectionincluding an evaporator 5 and a blower wheel or other fan 7 for drawingroom air over the evaporator coils and directing that air back into theroom as indicated by the arrow. The two sections of the unit areseparated and isolated by a wall or partition 9. The unit is adapted forinstallation in a room so that the evaporator section communicates withthe room air while the condenser section communicates with the outdoorair. The condenser and evaporator are part of a conventionalrefrigeration circuit which also includes a compressor and an expansiondevice (not shown), with the evaporator serving to absorb heat from roomair drawn over the evaporator coils by the blower, which then returnsthe cooled air back into the room. The heat absorbed by the refrigerantin the evaporator is thereafter transferred to the air being blownacross the condenser coils by fan 3. Partition 9 is located considerablycloser to blower wheel 7 than to fan 3, so that the pressure P in theregion of blower wheel 7 is less than pressure P on the condenser sideof partition 9. Both of pressures P and P are suction pressures and arethus below the ambient pressure P The pressure P above blower wheel 7 ishigher than the ambient pressure and is also higher than the pressure P,above fan 3 because of the relative characteristics of the two airmoving devices. An exhaust port 13 is defined in wall 9 between theregion of pressure P and the region of pressure P.;, so that when port13 is opened air flows through the port into the condenser section.Similarly, a vent port 15 is defined in wall 9 between'the region ofpressure P and the pressure of P, so that when port 15 is opened, airflows from the condenser section into the evaporator section andthereafter into the room. It is the means for opening and closing ports13 and 15 which are the subject of the present invention.

FIG. 2-4 illustrate apparatus for controlling the opening and closing ofports 13 and 15. The apparatus depicted enables the alternative openingof one of the ports and permits the closing of both ports; however, theapparatus is not adapted to open both ports simultaneously, since thiswould have the undesirable effect of simply circulating air between theports rather than transferring air to and from the room beingconditioned. An exhaust port door 17 has a portion 18 configured tocover and close exhaust port 13, and is mounted for pivotal movementabout an axis XX by a tab 19 extending through port 13. A tension spring21 is hooked at one end to a hole in tab 19 and at its other end to areceptacle 22 in a wall portion 23 of the unit. Spring 21 functions tobias door 17 to a closed position in which it covers port 13. Portion 23of wall 9 is bent back from the plane of the wall to enable the unit toaccommodate a control box 24 which contains the operating buttons or thelike for the unit. A second tab 25 includes a first section 27 which iscoplanar with portion 18, a second section 29 which is bent backtransversely to section 27 towards wall 23, and a third section 31 whichis generally parallel to section 27. The function of tab 25 will beapparent from the description to follow. A gasket 39 fabricated fromsome suitable material such as urethane foam is advantageously appliedto the door portion 18 engaging the wall surface surrounding dischargeport 13 when the door is moved to its discharge port closing position.The engagement of gasket 39 and the port edge enhances the degree towhich the door seals the port against the passage of air. In order toprevent any materials which could damage the air conditioning unit frompassing through discharge port 13, a filter 41 can be affixed across theport. Filter 41 may comprise a common filtering material such as finemesh screen.

Vent port 15 is disposed between condenser fan 3 and blower 7 to takeadvantage of the previously described pressure differential existing inthis area. A vent port door 43 is mounted for pivotal movement to openand close ventport l5. Vent door 43 includes a vent port closing portion47 which is dimensioned to shut port 15 to the passage of airtherethrough, and a tab 49 which extends through the vent port. Tab 49includes a first section 51 which is bent transversely to the plane ofvent port closing portion 47, a second section 53 which is bent fromsection 51 and is parallel to portion 47 and to section 27 of tab 25,and a third section 55 which is generally parallel to section 51. Tab 49serves the same purposes as both of tabs 19 and 25 associated with door17. A tension spring 57 is connected at one of its ends to anappropriately formed tab 59 in the housing of the air conditioning unit,and at its opposite end to a hole 61 in section 51 of tab 49. Spring 57biases vent port door 43 to the vent port closing position about thesame axis XX as door 17 is pivotable. F urthermore, by applying a forceto the upper face of tab 49 as viewed in the drawings, a torque tendingto open door 43 is exerted on this door. A gasket 63 fabricated from anappropriate material such as urethane foam is attached to door 43 forengaging the wall surface around vent port when door 43 is in its portclosing position. A filter 65 which can be in the form of a fine meshscreen is advantageously provided across vent port 15 for preventingpotentially damaging materials from passing through vent port 15 intothe evaporator section of the air conditioning unit.

In order to effect the selective opening and closing of the two ports,an operating lever 67 is provided in the unit. Lever 67 is preferably aunitary piece which can be fabricated from molded plastic, and comprisesan actuating arm 69 engageable with tabs 25 and 39 of the two doors, anda control arm 71 having a manually engageable portion 72 for operatingthe apparatus. Arms 69 and 71 extend transversely from a rotatable shaft73 having a longitudinal axis of rotation Y-Y which is parallel to thecommon axis of rotation X--X of exhaust port door 17 and vent port door43.

Actuating arm 69 includes at its end portion furthermost spaced fromshaft 73, a cylindrical portion 75 which is engageable with the tabportions of exhaust door 17 and vent door 43. Control arm 71 isangularly displaced from actuating arm 69 so that when the vent andexhaust doors are in their closed positions, manually engageable portion72 is centrally disposed in slot 77 in the exterior of control box 24.In other words, the foregoing elements are arranged such that when bothdoors are shut, control arm 71 is movable left or right as shown inFIGS. 2 and 3.

When both exhaust port door 17 and vent port door 43 are closed,cylindrical portion 75 of actuating arm 69 is in engagement withparallel sections 27 and 53 of the tabs of the two doors as indicated inFIG. 3. When control arm 71 is moved clockwise or to the left asindicated in the drawings to position A as indicated in FIG. 4, a forceis exerted transversely to section 53 of tab 49 of the vent door, withthe resulting torque causing door 43 to pivot about axis XX to open ventport 15. When control arm 71 has been so moved to a predeterminedextent, cylindrical portion 75 slides over section 53 onto section 55 asshown in FIG. 4. When this oc-' curs, the apparatus remains in thecondition shown in the drawing even after manual pressure is releasedfrom control arm 71. This is due to the configuration of tab section 55,which transfers the force exerted by spring 57 to operating lever 67such as to apply a clockwise torque on shaft 73. This torque urgescontrol arm 71 against a stop 81 which defines the end of slot 77. Thus,spring 57 biases vent door 43 to its closed position until cylindricalportion 75 slides onto tab section 55, after which door 43 is restrainedfrom closing by virtue of the force applied to the tab by portion 75.When control arm 71 is moved counterclockwise or to the right as shownin the drawings, spring 57 biases door 43 to its vent port closingposition after cylindrical portion 75 slides onto tab section 53, and ifcontrol arm 71 is released at this time, the vent door willautomatically close.

The operation of exhaust port door 17 is similar to the operation ofvent port door 43. Thus, as control arm 71 is moved counterclockwise ortowards the right as shown in the drawings, cylindrical portion 75 ofactuating arm 69 slides across section 27 of exhaust port door 17 andexerts a transverse force thereon. This action causes a clockwise torqueto be exerted on door 17, and the door is rotated about axis XX to anopen position. Cylindrical portion 75 eventually slides from section 27onto section 29, and finally reaches the juncture of sections 29 and 31in tab portion 25. At this time, the various elements are in thepositions shown by the phantom lines in FIG. 4. Until cylindricalportion 75 reaches the aforementioned juncture, spring 21 exerts acounterclockwise torque on door 17 and a clockwise torque on operatinglever 67, so that release of control arm 71 would result in theautomatic closing of exhaust port door 17. However, when cylindricalportion 75 reaches the juncture of sections 29 and 31, the torqueexerted on operating lever 67 becomes a counterclockwise torque urgingcontrol arm 71 against stop 82 defining the right-hand end slot 77. Therelease of manual pressure on control 71 at this point does not resultin the automatic closing of exhaust port door 17.

The location of operating lever 67 in control box 24 of the airconditioning unit facilitates the operation of the unit since all of thecontrols can be located in one portion of the machine. The extremesimplicity of the design of the apparatus for opening and closing thetwo ports in no way impairs the removal of control box 24 for repairs toparts in the box or in the region of the machine behind the box. Sinceactuating arm 69 is not attached to the two doors, operating lever 67can be moved out of engagement with tabs 25 and 49 with ease.

The design of the elements of the apparatus for opening and closing thedischarge and vent ports, and the relative location of these elements,make for a relatively simple construction of the apparatus. The springscan be stock items. Doors 17 and 43 can be stamped metal parts,appropriately treated thermo-plastic parts,

or the like. Operating lever 67 can be a molded plastic part asindicated earlier, or can be an appropriately cast part. The doors, andtheir associated springs can be assembled at the same time that otheritems are attached to the frame of the unit. Operating lever 67 canadvantageously be assembled to control box 24 before the box is attachedto the unit. The assembly of lever 67 with the other components of theapparatus can be accomplished by inserting actuating arm 69 between tabs25 and 49, and by locating shaft 73 in appropriate holes and slots inthe frame of the unit. To this end, a

series of collars 83 and 85 are provided for abutting mating surfaces inthe unit, and a leaf spring 87 which can be integral with operatinglever 67 is advantageously employed for cooperating with surfaces incontrol box 24 to hold shaft 73 in place. It is apparent from theforegoing that the assembly of this apparatus gn be easily accomplishedusing conventional assembly methods, and that the incorporation of theapparatus in an air conditioning unit does not necessitate changing thedimensions of the unit.

Several modifications to the embodiment described above can be used withthe invention. For example, the embodiment described above contemplatesthe provision of springs for biasing the exhaust and vent doors to theirclosed positions, and an operating lever for overcoming the bias of thesprings to open the doors. It is within the scope of the invention tobias the doors to their open positions, and to employ an operating leverfor selectively closing the doors. Also, it is within the scope of theinvention to incorporate but one of the two doors, in which case theconstruction and operation of the operating lever would accordingly bemodified to work in conjunction with that one door.

The invention has been described in detail with particular reference toa preferred embodiment thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

I claim: 1. In an air conditioning unit having a casing, a partitiondividing the unit into an evaporator section and a condenser section, anevaporator fan in the evaporator section of the unit and a condenserfari in the condenser section of the unit, the fans being disposed tocreate high and low pressure regions on the evaporator side of thepartition, apparatus for selectively venting outdoor air to a spacebeing conditioned or for exhausting from the space, said apparatuscomprising:

means defining an exhaust port in a region of the partition where thepressure on the evaporator side is higher than the pressure on thecondenser side;

an exhaust door for opening and closing said exhaust port;

means for mounting said exhaust door for pivotal movement betweenexhaust port opening and closing positions;

means defining a vent port in a region of the partition where thepressure on the evaporator side is lower than the region on thecondenser side;

a vent door for opening and closing said vent port;

means for mounting said vent door for pivotal movement between vent portopening and closing positions; and

lever means for operating said exhaust and vent doors, said lever meansincluding actuating means extending from a rotatable shaft forselectively engaging one of said exhaust and vent doors to apply torquethereto to effect the pivotal movement of said one door, and controlmeans extending transversely from said shaft for rotating the shaft.

2. Apparatus according to claim 1 wherein the mounting means associatedwith each of said discharge and vent doors is located adjacent therespective discharge and vent ports, and said doors each include a portclosing portion in the plane of the axis of pivotal movement of the doorfor covering the respective port and a second portion being engageableby said actuating means to effect the pivotal movement of the door.

3. Apparatus according to claim 1 and further including spring means forbiasing said vent and exhaust doors to their respective port closingpositions, wherein said lever means selectively applies torque to one ofsaid vent and exhaust doors to open said one door against the force ofsaid spring means.

4. Apparatus according to claim 3 wherein the spring means for biasingsaid vent and exhaust doors each comprise a tension spring connected atone end to the respective exhaust and vent door and at the opposite endto said partition.

5. Apparatus according to claim 1 and further comprising:

means for biasing said exhaust door to either the exhaust port openingposition or the exhaust port closing position; and means for biasingsaid vent door to the same of the port opening or closing positions assaid exhaust door biasing means biases said exhaust door;

wherein said exhaust door mounting means and said vent door mountingmeans mount said doors for pivotal movement about parallel axes;

and wherein said rotatable shaft has a longitudinal axis of rotationparallel to the axes of pivotal movement of said doors, and said controlmeans has a manually accessible portion, movement of said control meansrotating said shaft to apply torque to a selected one of said doorsagainst the biasing means associated with said one door.

6. Apparatus according to claim 1 and further including means forbiasing at least one of said exhaust and vent doors to its respectiveport opening or port closing position; wherein: V v

said one door includes a port closing portion and a tab extending fromsaid port closing portion, said tab including a first section engageableby said actuating means for effecting movement of said one door againstthe biasing means associated with said one door, and a second sectiontransverse to said first section, said second section being engageableby said actuating means for maintaining said one door in the .positionto which said actuating means has moved said one door.

7. Apparatus according to claim 1 and further including means forbiasing each of said exhaust and vent doors to one of their port openingor port closing positions; wherein:

each of said doors includes a port closing portion and a tab extendingfrom said port closing portion, said tab having a first sectionengageable by said actuating means for effecting movement of said dooragainst the biasing means associated with said door, and a secondsection transverse to said first section, said second section beingengageable by said actuating means for maintaining said door in theposition to which said actuating means has moved said door.

8. Apparatus according to claim 7 wherein the first sections of saidtabs are located in a generally opposed relationship, and said actuatingmeans comprises an arm disposed between said tabs for alternativelyexerting torque on said tabs to selectively move one of said doors.

1. In an air conditioning unit having a casing, a partition dividing theunit into an evaporator section and a condenser section, an evaporatorfan in the evaporator section of the unit and a condenser fan in thecondenser section of the unit, the fans being disposed to create highand low pressure regions on the evaporator side of the partition,apparatus for selectively venting outdoor air to a space beingconditioned or for exhausting from the space, said apparatus comprising:means defining an exhaust port in a region of the partition where thepressure on the evaporator side is higher than the pressure on thecondenser side; an exhaust door for opening and closing said exhaustport; means for mounting said exhaust door for pivotal movement betweenexhaust port opening and closing positions; means defining a vent portin a region of the partition where the pressure on the evaporator sideis lower than the region on the condenser side; a vent door for openingand closing said vent port; means for mounting said vent door forpivotal movement between vent port opening and closing positions; andlever means for operating said exhaust and vent doors, said lever meansincluding actuating means extending from a rotatable shaft forselectively engaging one of said exhaust and vent doors to apply torquethereto to effect the pivotal movement of said one door, and controlmeans extending transversely from said shaft for rotating the shaft. 2.Apparatus according to claim 1 wherein the mounting means associatedwith each of said discharge and vent doors is located adjacent therespective discharge and vent ports, and said doors each include a portclosing portion in the plane of the axis of pivotal movement of the doorfor covering the respective port and a second portion being engageableby said actuating means To effect the pivotal movement of the door. 3.Apparatus according to claim 1 and further including spring means forbiasing said vent and exhaust doors to their respective port closingpositions, wherein said lever means selectively applies torque to one ofsaid vent and exhaust doors to open said one door against the force ofsaid spring means.
 4. Apparatus according to claim 3 wherein the springmeans for biasing said vent and exhaust doors each comprise a tensionspring connected at one end to the respective exhaust and vent door andat the opposite end to said partition.
 5. Apparatus according to claim 1and further comprising: means for biasing said exhaust door to eitherthe exhaust port opening position or the exhaust port closing position;and means for biasing said vent door to the same of the port opening orclosing positions as said exhaust door biasing means biases said exhaustdoor; wherein said exhaust door mounting means and said vent doormounting means mount said doors for pivotal movement about parallelaxes; and wherein said rotatable shaft has a longitudinal axis ofrotation parallel to the axes of pivotal movement of said doors, andsaid control means has a manually accessible portion, movement of saidcontrol means rotating said shaft to apply torque to a selected one ofsaid doors against the biasing means associated with said one door. 6.Apparatus according to claim 1 and further including means for biasingat least one of said exhaust and vent doors to its respective portopening or port closing position; wherein: said one door includes a portclosing portion and a tab extending from said port closing portion, saidtab including a first section engageable by said actuating means foreffecting movement of said one door against the biasing means associatedwith said one door, and a second section transverse to said firstsection, said second section being engageable by said actuating meansfor maintaining said one door in the position to which said actuatingmeans has moved said one door.
 7. Apparatus according to claim 1 andfurther including means for biasing each of said exhaust and vent doorsto one of their port opening or port closing positions; wherein: each ofsaid doors includes a port closing portion and a tab extending from saidport closing portion, said tab having a first section engageable by saidactuating means for effecting movement of said door against the biasingmeans associated with said door, and a second section transverse to saidfirst section, said second section being engageable by said actuatingmeans for maintaining said door in the position to which said actuatingmeans has moved said door.
 8. Apparatus according to claim 7 wherein thefirst sections of said tabs are located in a generally opposedrelationship, and said actuating means comprises an arm disposed betweensaid tabs for alternatively exerting torque on said tabs to selectivelymove one of said doors.